Brown the beef (optional):
In a skillet over medium heat, cook ground beef until browned. Drain excess fat and transfer to the slow cooker.
Add the base:
Into the slow cooker, add beef broth, milk, tomato paste, paprika, garlic powder, onion powder, salt, and pepper. Stir to combine.
Cook low and slow:
Cover and cook on LOW for 3 hours.
Add pasta:
Stir in uncooked pasta. Cover again and cook for 30–40 minutes, until pasta is tender. Stir once halfway through if possible.
Add cheese:
Turn off heat. Stir in shredded cheddar cheese (and cream cheese if using). Let sit for 5–10 minutes to thicken.
Serve:
Taste and adjust seasoning if needed. Serve hot and garnish with parsley if desired.